Typically, graft copolymers of olefin polymer materials have been impact modified with ethylene/propylene copolymer rubber, ethylene/propylene/diene monomer rubber, and ASA polymers. For example, U.S. Pat. No. 3,314,904 describes forming a "gum plastic" by making a graft copolymer of styrene on polyethylene or polypropylene, and, in particular, a graft interpolymer of styrene, acrylonitrile, and polyethylene or polypropylene, and blending the graft copolymer with certain selected compatible rubbery materials. The grafted styrene or styrene/acrylonitrile content of the graft copolymer is 75-95%, preferably 85-95%, and more preferably 90-95%. Hence the graft copolymer is predominantly bound styrene or bound styrene/acrylonitrile, and in the graft copolymers made from polypropylene, the polypropylene is only a minor component and present as a dispersed phase. Thus the properties of the bound styrene or styrene/acrylonitrile predominate. The graft copolymer is made by subjecting the polyolefin to high-energy ionizing radiation, and then contacting the irradiated polyolefin with styrene or with styrene and acrylonitrile.
U.S. Pat. No. 4,537,933 discloses a blend of a polyolefin graft polymer, preferably a polyvinyl halide polyolefin graft polymer, and an ASA polymer. The ASA polymer is a copolymer of styrene and acrylonitrile (SAN) that is modified with an acrylate polymer, a chlorinated polyethylene or an olefin-diolefin modified polymer, such as an ethylene/propylene polyene modified polymer. The ASA polymer modified with the olefin-diolefin modified polymer has a styrene/acrylonitrile content of 60-95%. The properties of the SAN predominate since the rubber is only a minor component and present as a dispersed phase. Also, the matrix phase of the polymeric components must be miscible.
The advantages of graft copolymers of a polymerizable monomer(s) on a propylene polymer backbone over physical blends of the polymers as stand-alone structural plastics could be better utilized if a means were found for imparting a better balance of properties to the graft copolymers.
Various compositions have been obtained in an attempt to achieve a better balance of properties. For example, U.S. Pat. No. 4,990,558 discloses a graft copolymer based rigid thermoplastic composition of (a) from 60 to 95%, by weight, of a graft copolymer of a styrenic polymer grafted onto a propylene polymer material backbone and (b) from 5 to 40%, by weight, of a rubber component comprising (1) from 20 to 100%, by weight, of (i) at least one monoalkenyl aromatic hydrocarbon-conjugated diene block copolymer, (ii) at least one block copolymer which is a hydrogenated copolymer of (i), or (iii) a mixture of at least one (i) with at least one (ii); and (2) 0 to 80%, by weight, of an olefin copolymer rubber, i.e. EPM or EPDM.
U.S. Pat. No. 5,286,791 discloses impact modified graft copolymer compositions comprising (A) from 10 to 90% of a graft copolymer of propylene polymer material having graft polymerized thereto one or more vinyl monomer(s); (B) from 90 to 10% of at least one broad molecular weight distribution propylene polymer material having a M.sub.w /M.sub.n of 8 to 60, a melt flow rate of 0.5 to 50 and a xylene insolubles at 25.degree. C. of greater than or equal to 94%; and (C) from 2 to 25% of at least one rubber component selected from (i) an olefin rubber containing two or more monomers selected from ethylene, propylene or butene, and optionally a non-conjugated diene, (ii) one or more monoalkenyl aromatic hydrocarbon-conjugated diene block copolymer or hydrogenated products thereof, (iii) a graft copolymer of propylene polymer material grafted with polymerizable monomer(s) which when polymerize form a rubbery polymer(s) having a Tg less than 20.degree. C., and (iv) mixtures thereof.
In U.S. Pat. No. 5,397,836, there is disclosed thermoplastic blends comprising (A) 40 to 90% of a graft copolymer of a propylene polymer material having a polymerized monomer content of 5 to 70% and (B) 5 to 40% of a graft copolymer of an olefin rubber material having a polymerized monomer content of 5 to 50%, wherein the grafting monomer(s) are selected from the group consisting of (i) an aromatic vinyl compound, (ii) an acrylic compound, (iii) mixtures of (i) and (ii), and (iv) other copolymerizable monomers selected from the group consisting of C.sub.1-10 linear or branched alkyl acrylates, acrylic acid, methacrylic acid, glycidyl methacrylate, glycidyl acrylate, acrylonitrile and methacrylonitrile with at least one (i) or at least one (ii) or mixtures of at least one (i) and at least one (ii) wherein said other copolymerizable monomer being present in an amount of up to 50% and (C) 5 to 20% of an ungrafted olefin rubber selected from (i) an olefin rubber containing two or more monomers selected from ethylene, propylene or butene, and optionally a non-conjugated diene, (ii) a propylene homopolymer or random copolymer of propylene and an olefin selected from ethylene and C.sub.4 -C.sub.10 alpha-olefin impact modified with (1) defined above.
However, while a better balance of properties is obtained there is still some loss in weldline strength and retention thereof.
Thus, an impact modified graft copolymer composition having an overall balance of properties without a substantial loss in weldline strength and weldline strength retention is desired.